GaN-based high electron mobility transistors (HEMTs), due to a high concentration of two-dimensional electron gas (2DEG) and a high breakdown voltage, have attracted extensive attention from scientific research institutes and enterprises. It is one of the greatest challenges in the research of GaN-based HEMTs to make the breakdown voltage as high as possible while maintaining a low on-resistance.
GaN-based HEMT devices usually have planar structures. When the HEMT is in the OFF state, a negative bias is applied to the gate electrode, a positive bias is applied to the drain electrode, and the source electrode is grounded. This results in concentration of electric field lines at an edge of a side of the gate electrode close to the drain electrode, such that an electric field peak is formed. When the voltages applied to the gate electrode and to the drain electrode are gradually increased, the electric field peak at the edge of the gate electrode is further increased. The device will be broken down here when the applied voltage is higher than the critical breakdown electric field strength.